1. Field
The present invention relates generally to data communication, and more specifically to techniques for processing data for transmission in a wireless communication system using selective channel transmission and defined (e.g., uniform) transmit power allocation.
2. Background
A multi-channel communication system is often deployed to provide increased transmission capacity for various types of communication such as voice, data, and so on. Such a multi-channel system may be a multiple-input multiple-output (MIMO) communication system, an orthogonal frequency division modulation (OFDM) system, a MIMO system that utilizes OFDM, or some other type of system. A MIMO system employs multiple transmit antennas and multiple receive antennas to exploit spatial diversity to support a number of spatial subchannels, each of which may be used to transmit data. An OFDM system effectively partitions the operating frequency band into a number of frequency subchannels (or frequency bins), each of which is associated with a respective subcarrier on which data may be modulated. A multi-channel communication system thus supports a number of xe2x80x9ctransmissionxe2x80x9d channels, each of which may correspond to a spatial subchannel in a MIMO system, a frequency subchannel in an OFDM system, or a spatial subchannel of a frequency subchannel in a MIMO system that utilizes OFDM.
The transmission channels of a multi-channel communication system typically experience different link conditions (e.g., due to different fading and multipath effects) and may achieve different signal-to-noise-plus-interference ratios (SNRs). Consequently, the transmission capacities (i.e., the information bit rates) that may be supported by the transmission channels for a particular level of performance may be different from channel to channel. Moreover, the link conditions typically vary over time. As a result, the bit rates supported by the transmission channels also vary with time.
The different transmission capacities of the transmission channels plus the time-variant nature of these capacities make it challenging to provide an effective coding and modulation scheme capable of processing data prior to transmission on the channels. Moreover, for practical considerations, the coding and modulation scheme should be simple to implement and utilize at both the transmitter and receiver systems.
There is therefore a need in the art for techniques to effectively and efficiently process data for transmission on multiple transmission channels with different capacities to improve performance and reduce complexity.
Aspects of the invention provide techniques to select transmission channels for use for data transmission and to process and transmit data over the selected transmission channels. In certain embodiments, the transmission channels available for use may be segregated into one or more groups, with each group including any number of transmission channels. For a MIMO system that utilizes OFDM, the available transmission channels correspond to the spatial subchannels and frequency subchannels, each group may correspond to, for example, a respective transmit antenna, and the transmission channels in each group may be the frequency subchannels for the corresponding transmit antenna.
In an aspect, which is referred to as selective channel transmission (SCT), only xe2x80x9cgoodxe2x80x9d transmission channels in each group are selected for use for data transmission, and xe2x80x9cbadxe2x80x9d transmission channels are not used. The good transmission channels may be defined as those having SNRs or power gains at or above a particular SNR or power gain threshold. The total available transmit power for each group is then distributed amongst the good transmission channels in accordance with a defined allocation scheme. In an embodiment, the defined allocation scheme uniformly distributes the total available transmit power amongst the good transmission channels. Other allocation schemes may also be used.
In another aspect, the selective channel transmission may be used in conjunction with common coding and modulation, which would then simplify the coding/modulation at a transmitter system and the complementary demodulation/decoding at a receiver system. Each group of transmission channels may be associated with a respective coding and modulation scheme, and data for each group may be coded and modulated based on the scheme selected for the group. Each group may thus be associated with (1) a respective (e.g., SNR or power gain) threshold used to select transmission channels for use for data transmission and (2) a respective coding and modulation scheme used to process data for the group.
The selective channel transmission may provide improved performance due to the combined benefits of (1) using only the best transmission channels in each group, which are selected from among all available transmission channels in the group, (2) allocating the total available transmit power amongst only the selected transmission channels, and (3) matching the data processing for the selected transmission channels to the capacity achievable for these channels.
The invention further provides methods, systems, and apparatus that implement various aspects, embodiments, and features of the invention, as described in further detail below.